The present disclosure relates to rotary-winged aircraft. More specifically, the present disclosure relates to helicopters with high-speed operational capabilities.
Helicopters have historically suffered from low operational cruise speeds, of up to about 160 knots. To increase the speed of operation of a conventional helicopter above that threshold, there is a tendency to increase a main rotor forward tip angle relative to the freestream airflow, which results in a high degree of main rotor flapping, reduced propulsive efficiency, reduced rotor stall margin, and reduced lift-to-drag ratio. Further, a negative fuselage angle of the helicopter relative to the freestream airflow is increased, the overall result being that the fuselage is downloaded, which requires yet more rotor power to overcome. The conventional tail of the helicopter including a conventional tail rotor adds drag due to the tail rotor hub position and tail rotor H-force drag, also requiring increased main rotor power to overcome.
Historically helicopters have included a wing extending from the fuselage to provide additional lift at the fuselage to compensate for the download and to increase stall margin of the main rotor. Including a wing, however, also often compromises helicopter design in other ways. First, the addition of the wing increases empty weight of the helicopter and increases vertical drag during hover operation. This results in lower payload capabilities and increased cost due to the additional components. The wing also increases parasitic drag during cruise operations, thus increasing cruise power required to attain the high speed operation and also increasing fuel burn. Finally, the physical size and location of the wing on the fuselage makes positioning of components such as cargo doors and rescue hoists difficult. The wing inhibits personnel movement aboard the helicopter, blocks visibility, and makes shipboard operations, where components such as main rotors are folded to save space, difficult.